A separate vacuum motor controls the central doorlock. The vacuum that is generated by the engine controls the height adjustable headlights. You can practically hook it up to every possible vacuum line you see coming from the engine bay.
You don't want to connect the headlight leveling to the doorlock system since the doorlock vacuum motor only gets engaged once the car is (un)locked.

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)